1. Field of the Invention
The present invention relates to a display system and, more particularly, to a display system including a spatial light modulator (SLM).
2. Description of the Related Art
A display system has been known in which a light beam whose intensity is modulated with a signal of information, is projected onto a screen by a optical projector system to display a two-dimensional image of the information. In this respect, a conventional system utilizes an optical beam whose intensity is modulated according to pixel data of the image carried by an image signal, and the optical beam scans a display screen vertically and horizontally. With these prior art techniques, it has been impossible to form a two-dimensional high-definition optical image with high brightness such as a two-dimensional image consisting of 4000.times.4000 pixels substantially on a real-time basis, because a signal conversion device satisfying this requirement has been unavailable.
In an attempt to solve the foregoing problem, the present Applicant has proposed an improved system as described in Japanese patent application No. 337171/1989 corresponding to U.S. patent application Ser. No. 633,223, now U.S. Pat. No. 5,185,617. In particular, a light source projects light rays of a rectilinear cross section onto a linear light modulator, in which the incident light rays are intensity-modulated correspondingly with pixels of information aligned in the linear light modulator, in turn, the intensity modulated light rays leave the light modulator as a light beam of a rectilinear cross section. The outgoing beam is deflected horizontally at a given frequency by a rotating polygon mirror and projected onto a screen via a projector lens to create a two-dimensional image. The aforementioned problem is solved by this conventional system. This improved system makes it easy to display a high-definition image with high brightness.
However, the system proposed by the present Applicant as described above has a disadvantage that the intensity modulation of light in the light modulator according to the pixels of information, is slow in response. To solve the problem of this slow response, the present Applicant has proposed another display system as described in Japanese patent application No. 130498/1990 corresponding to U.S. patent application Set. No. 702,817. Specifically, a stream of information to be displayed as a two dimensional image, is divided into plural pieces. A linear array of light-emitting devices is arranged to have N light-emitting devices corresponding to N pixels contained in each divided piece of the stream of information. During a given period, the N light-emitting devices are driven with each divided piece of information as such that signals of N pixels in each divided piece of the information are concurrently supplied to their respective N light-emitting devices to light up them simultaneously and according to each divided piece of information. Light rays emitted from the array of light-emitting devices are concurrently deflected in a direction perpendicular to the direction of the array of the light rays. These deflected light rays impinges as writing light onto a spatial light modulator comprising at least a photoconductive layer and a light modulation layer interposed between electrodes. The writing light is focused onto the photoconductive layer. Reading light is arranged to impinge the spatial light modulator to project the image information read from the modulator onto a screen.
If the reading light used to read the information from the spatial light modulator leaks into the photoconductive layer of the modulator on which the reading light impinges, then the contrast ratio deteriorates. However, it is impossible to design the modulator so that the leakage of the reading light is completely eliminated. Where a bright and good quality image is desired to be displayed on the display system of this construction, an intense reading light in the visible region must be directed to the spatial light modulator. In this case, the amount of the reading light leaking into the photoconductive layer of the modulator increases. As a result, it is inevitable that the contrast of the displayed image reduces. When a high resolution and high quality image writing is desired under such condition that a large amount of reading light leaks into the photoconductive layer of the modulator as described above, one of the conceivable methods is using an intense light beam of a small diameter as the writing light. However, it is difficult to produce such writing light from light-emitting devices forming an array.